弹簧关节

extends Node

const REST_LENGTH: float = 180.0
const BOB_RADIUS: float = 40.0

const SPRINGS: Array = [
	{stiffness = 4.0, damping = 0.2, color = '#8da5f3'},
	{stiffness = 14.0, damping = 0.6, color = '#8eef97'},
	{stiffness = 40.0, damping = 2.0, color = '#fc7f7f'},
]

var bobs: Array[RigidBody2D] = []
var anchors: Array[Vector2] = []
var cords: Array[Line2D] = []


func _ready() -> void:
	_add_background()

	var view: Vector2 = get_viewport().get_visible_rect().size

	for i in SPRINGS.size():
		var top: Vector2 = Vector2(view.x * (i + 1) / (SPRINGS.size() + 1), view.y * 0.2)

		var anchor: StaticBody2D = StaticBody2D.new()
		anchor.position = top
		anchor.add_child(_make_rect(Vector2(70, 16), Color('#2a2f3d')))
		add_child(anchor)

		var bob: RigidBody2D = _add_bob(top + Vector2(0, REST_LENGTH + 120), Color(SPRINGS[i].color))

		var spring: DampedSpringJoint2D = DampedSpringJoint2D.new()
		spring.position = top
		spring.length = REST_LENGTH * 2.0
		spring.rest_length = REST_LENGTH
		spring.stiffness = SPRINGS[i].stiffness
		spring.damping = SPRINGS[i].damping
		add_child(spring)

		spring.node_a = anchor.get_path()
		spring.node_b = bob.get_path()

		var cord: Line2D = Line2D.new()
		cord.width = 3.0
		cord.default_color = Color('#2a2f3d')
		cord.points = PackedVector2Array([top, bob.position])
		add_child(cord)

		bobs.append(bob)
		anchors.append(top)
		cords.append(cord)

	print('same rest length, three stiffness and damping pairs')


func _process(_delta: float) -> void:
	for i in bobs.size():
		cords[i].points = PackedVector2Array([anchors[i], bobs[i].position])


func _add_bob(at: Vector2, color: Color) -> RigidBody2D:
	var circle: CircleShape2D = CircleShape2D.new()
	circle.radius = BOB_RADIUS

	var collision: CollisionShape2D = CollisionShape2D.new()
	collision.shape = circle

	var bob: RigidBody2D = RigidBody2D.new()
	bob.position = at
	bob.add_child(_make_circle(BOB_RADIUS, color))
	bob.add_child(collision)
	add_child(bob)

	return bob


func _make_rect(size: Vector2, color: Color) -> Polygon2D:
	var rect: Polygon2D = Polygon2D.new()
	rect.polygon = PackedVector2Array([-size * 0.5, Vector2(size.x, -size.y) * 0.5, size * 0.5, Vector2(-size.x, size.y) * 0.5])
	rect.color = color

	return rect


func _make_circle(radius: float, color: Color) -> Polygon2D:
	var points: PackedVector2Array = PackedVector2Array()

	for i in 24:
		points.append(Vector2(cos(TAU * i / 24.0), sin(TAU * i / 24.0)) * radius)

	var circle: Polygon2D = Polygon2D.new()
	circle.polygon = points
	circle.color = color

	return circle


func _add_background() -> void:
	var background: ColorRect = ColorRect.new()
	background.color = Color('#12141a')
	add_child(background)
	background.set_anchors_and_offsets_preset(Control.PRESET_FULL_RECT)